It has been disclosed in the above-identified applications and patents that certain crystalline layered mixed metal hydroxides and activated mixed metal hydroxides can be used in the modification of the viscosity of various fluid formulations. In some of the disclosures, the said mixed metal hydroxides are combined with clay, e.g. bentonite and others, and with fine-particle silica, to form adducts which are useful for viscosity modification of drilling fluids and other fluids. In some cases, the viscosity is said to be thixotropic, and in other cases the viscosity is merely said to be thickened or modified. Also, some of the above-identified pending applications disclose that fluids gelled by use of the crystalline layered mixed metal hydroxides will quickly re-gel after being subjected to shear.
In a paper prepared for presentation at the 1990 Drilling Conference of the International Association of Drilling Contractors/Society of Petroleum Engineers in Houston, Tex., Feb. 27-Mar. 2, 1990 , the efficacy of using MMH (Mixed Metal Hydroxides) in a drilling mud are disclosed. The paper, in its References section on page 5, refers to other papers about the use of MMH in drilling muds at meetings of the IAPC/SPE and SPE Symposium on Oilfield Chemistry in February-March 1989. These publications are cumulative to the information disclosed in U.S. Pat. Nos. 4,664,843 and 4,790,954, the publication of which pre-dates these papers.
None of the patents identified above disclose any recognition of an entirely novel type of viscosity effect which is not of the forms previously known, i.e, those known to rheologists as dilatant, thixotropic, Newtonian, non-Newtonian, psuedo-plastic, Bingham plastic, or rheopexic.
Other related patents are U.S. Pat. Nos. 4,822,421; 4,990,268; 4,999,025; and 5,015,409, this latter patent being a continuation-in-part of the above-cited Ser. No. 060,133, now U.S. Pat. No. 4,990,268, which is a continuation of application Ser. No. 7,52,325, field Jul. 5, 1985, now abandoned.
We have now discovered more about some of these reported compounds and formulations containing them and have discovered some which undergo a phase change from an elastic solid state to a fluid state under the force of stress, rather than shear, and which immediately revert to an elastic solid state upon cessation of the stress: this is an unexpected phenomenon, which we believe has not been previously recognized or reported by others, and is believed to be unique. In a manner of speaking, it is a phase metamorphosis, not a chemical metamorphosis.
The phase change of going from an elastic solid phase to a fluid phase by the applying a fluidizing amount of stress, and then reversion back to the elastic solid phase upon cessation of the stress, is not perceived as a viscosity modification in the ordinary sense of the term "viscosity modification".
For example, changing of a Newtonian liquid to a non-Newtonian liquid, or vice-versa, is one form of a viscosity modification. Changing the degree or extent of thixotropicity or dilatancy of a liquid is a form of viscosity modification. These viscosity modifications are not perceived as being a phase change from an elastic solid phase to a fluid phase.
Instead, our new discovery is perceived as a reversible phase change of an elastic solid composition having high energy, short range ionic interactions with a very low degree of reinforcement. Because of this a stress-induced fluidization of the elastic solid is reversible, since the high energy, short range interactions are not destroyed, and the low degree of reinforcement permits the fluidization until reversion back to an elastic solid.
These elastic solids having reversible stress-induced fluidity are perceived as being analogous, in their response to a critical stress, to a solid-state diode in response to a flow of electrons and the cessation of the flow of electrons.
This novel phase change effect is herein given the name of "stress-dependent fluidity" as a means of identifying the effect on an elastic solid which instantly becomes a relatively low-viscosity fluid under a critical stress. The change from an elastic solid phase to a fluid phase begins as soon as the critical stress is applied and the reversion to an elastic solid phase is immediate upon ceasing the stress; by "immediate" it is meant that the reversion to the elastic solid state is a fraction of a second, essentially too fast for visual perception or for measurement using state of the art measuring devices. It is not the same effect as is obtained using shearing forces to break up a gel or a sol since those do not immediately return to the form of a gel or sol, (such as hydrogel, alcogel, organogel, or electrosol) though many will return, at least to some degree, to a gel or sol over a detectable period of time. Some of the various previously known forms of gels or sols may even undergo changes under shearing forces which interfere with, or even prevent a complete return to their previous form upon cessation of the shearing forces.